Surgical implant for spinal fixation

Abstract: A surgical implant for spinal fixation comprising a rigid biocompatible frame (1) defining an aperture (6), the frame consisting of first and second substantially parallel frame portions (2, 3) connected by bent third and fourth frame portions (4, 5), extending in the same direction as each other away from the plane defined by the first and second frame portions (2, 3), whereby at least one of the third and fourth frame portions being curved (5) away from the opposing frame portion so as to define a tapered portion of relatively small width which, in use, can be fitted closely about the spine.

Description: This invention relates to surgical implants for spinal fixation. Spinal fixation implants are used to correct abnormal curvature of, and/or impart stability to, the spine by immobilising a plurality of vertebrae with respect to each other. A rigid frame which fits neatly onto the posterior surface of the spine to embrace at least two adjacent vertebrae is fixed in place by means of fixation wires (or cables) passed around or looped through the frame and passed under the laminae to immobilise the embraced vertebrae with respect to each other. One type of know spinal fixation implant comprises stainless steel or titanium rods formed into a rectangle. The fixation wires are looped around the rod formed into a rectangle. The fixation wires are looped around the rod to secure the rectangle to the spine. EP-A-146347 discloses a surgical implant for spinal fixation comprising a rigid biocompatible frame defining an aperture, the frame consisting of first and second substantially parallel frame portions connected by bent third and fourth frame portions which oppose each other across the space between the first and second parallel frame portions, the third and fourth frame portions extending in the same direction as each other away from the plane defined by the first and second frame portions. A problem of prior art implants is the dead space between a fitted implant and the spine arising from a lack of conformity between the contours of the cervical spine and the spinal implant. The present invention provides a surgical implant as defined in claim 1. In a preferred form, the frame defines a bullet-shaped aperture, that is, three sides of the frame, when viewed from above, define a substantially rectangular space which is extended at one end towards a point defined by either straight or curving converging frame portions. Preferably the frame is formed from titanium alloy (Ti-6Al-4V) sheet stock and has flat surfaces. Embodiments of the present invention will now be described, by way of example, and with reference to the accompanying drawings, in which : FIGURE 1 is a plan view of a surgical implant embodying the present invention; FIGURE 2 is a section along line II-II of Figure 1; FIGURE 3 is a side view of the implant of Figure 1; FIGURE 4 is a section along line IV-IV of Figure 1; FIGURE 5 illustrates one of the slots in the implant of Figure 1; FIGURES 6 and 7 are plan and side views respectively of an alternative embodiment of the present invention; FIGURES 8 and 9 are plan and side views respectively of a further alternative embodiment of the present invention; FIGURES 10, 11 and 12 are plan views of further alternative embodiments of the present invention; FIGURE 13 is a plan view of an alternative embodiment of a surgical implant embodying the present invention; FIGURE 14 is a side view of the surgical implant of Figure 13; FIGURE 15 is a plan view of an alternative embodiment of the present invention; FIGURE 16 is a side view of the surgical implant of Figure 15; FIGURE 17 is a section along line XIX-XIX of Figures 13 or 15; FIGURE 18 is a section similar to that of Figure 6 through an alternative frame construction; and FIGURE 19 is an end view of the surgical implants of Figures 13 and 15. Referring to Figures 1 to 3, a titanium alloy frame (1) having first and second substantially parallel frame portions (2, 3) respectively, connected by third and fourth bent shorter end frame portions (4, 5) respectively, defines an aperture (6) for receiving projecting spinal elements. The frame (1) has recesses, such as, slots (7) and grooves (8), for receiving fixation wires or cables. The frame (1) is formed from titanium alloy (Ti-6Al-4V) sheet stock. The frame portions (2,3,4,5) are each approximately 0.35 inches (0.9cm) wide and 0.125 inches (0.3 cm) thick. All the frame edges are either chamfered or rounded (see Figure 4). Referring to Figure 1, the first frame end portion (4) curves slightly into the aperture (6) defining wire seats (9), and the second frame end portion (5) is semi-circular. The frame (1) is approximately 2.35 inches (6 cm) in length from the top of the second end portion (5) to the bottom of the first end portion (4) with the second end portion (5) being defined by a circle of approximately 0.72 inches (1.83 cm) radius. The aperture (6) is approximately 0.8 inches (2 cm) wide. The parallel frame portions (2, 3) may each have three recesses, such as slots (7), in the frame edge (11) remote from the aperture (6). The slots (7) are spaced approximately 0.55 inches (1.4 cm) apart on each parallel frame portion (2, 3) with the slots closest to the second end portion (5) being approximately 0.72 inches (1.83 cm) from the top of the second end portion (5). Referring to Figure 5, each slot (7) has its centre line substantially orthogonal to the frame edge (11) remote from the frame aperture (6) and is defined by an opening (16), 0.08 inches (0.2 cm) wide in the frame edge (11) which communicates with a cylindrical hole (17) 0.055 inches (0.14 cm) inches in radius having its centre 0.065 inches (0.165 cm) from the frame edge (11). The second end portion (5) has two grooves of semi-circular section in the frame edge (12) adjacent to the frame aperture (6). Each groove (8) is defined by a circle approximately 0.055 inches (0.14 cm) in radius having its centre on the frame edge (12) adjacent the frame aperture (6) approximately 0.41 inches (1.04 cm) below the top of the second end portion (5). The middle section (10) of each of the end portions (4, 5) bends through an angle of approximately 100° (preferably 102°) as shown in Figure 2, and the parallel frame portions (2, 3) of the frame (1) curve as shown in Figure 3 so as to accommodate lordosis (or kyphosis) in the spine. The lordotic curve of frame (1) is defined by an arc of a circle, the radius of the circle being in the range 5 to 7 inches (13.2 to 17.8 cm). Preferably, the frame (1) of length 2.35 inches (6 cm) is available in three different lordotic curvatures: flat, arc of a circle of 5 inches (13,2 cm) radius and arc of a circle of 7 inches (17,8 cm) radius. In use, the titanium alloy frame (1) is placed over the spinous processes on the lamina with the substantially parallel frame portions (2, 3) lying substantially parallel to the spine axis with vertebrae elements (the spinous processes) being received in the frame aperture (6). The vertebrae received within the frame (1) are immobilised with respect to each other and the frame (1) by fixation wires or cables looped around the frame (1) and around the lamina of adjacent vertebra. Fixation wires or cables are looped through the recesses) (slots (7), grooves (8) and/or at wire seats (9). Whereas in the prior art spinal implants the looped fixation wires or cables are prone to slip parallel to the frame portion around which they are looped, in the frame (1) of the present invention the fixation wires or cables are secured within a recess, slot (7) or groove (8), and can therefore resist forces parallel to the frame portion around which they are looped. The frame (1) of the present invention can therefore be rigidly anchored to the spine. As will be seen from the drawings, the preferred form of frame is symmetrical about a central plane along the longitudinal axis of the device (A-A in Figure 1), having long portions (2, 3) which are substantially parallel (when viewed from above) to the longitudinal axis A-A, and interconnecting portions at either end. The interconnecting portions at each end are asymmetrical about an axis B-B, see Figure 3; one (5) a continuous tapering arc connecting the long sides (2,3) to define a converging region of somewhat 'pointed' shape, and the other (4) a substantially straight portion at approximately 90° to the long portions. As a whole, when viewed as in Figure 1, the frame defines an aperture similar in shape to a bullet. When viewed from the side, see Figure 3, the long sides of the loop formed by the frame are coplanar and shaped to form a curve which roughly approximates the curve of the spine. In end view, Figure 2, the interconnecting portions (4, 5) extend out the plane of the long sides, defining a rise at either end, having apex in the plane A-A shown in Figure 1. The bullet shaped implant (1) of rectangular cross-section has superior conformance, at the upper and lower ends of the cervical spine, to the contours of the cervical spine. The bullet shaped frame (1) can be used pointing to the head in the lower cervical spine, while at the craniovertebral junction, its reversal, to allow the substantially straight end frame portion (4) to nestle against the occiput provides an excellent fixation for the craniovertebral junction. The slots (7) on the frame (1) about every 1.5 cm are compatible with Titanium cable and, by fixing sublaminar cables though the slots (7) provide an extremely firm fixation far in excess to that provided by the conventional prior art frame arrangement. Figures 6 and 7 illustrate a titanium frame (18) similar to that of Figures 1 to 4 but having substantially parallel frame portions (19, 20) of different dimensions. The frame (18) is approximately 1.57 inches (4 cm) in length from the top of the second end portions (5) to the bottom of the first end portion (4). The substantially parallel frame portions (19, 20) each have two slots (7) into the frame edge (11) remote from the frame aperture (6), with the slots (7) being spaced approximately 0.55 inches (1.4 cm) apart and the slot closest to the second end portion (5) being approximately 0.6 inches (1.5 cm) from the top of the second end portion (5). Preferably, the frame (18) of Figures 6 and 7 is available in three different lordotic curvatures; flat, arc of a circle of 4 inches (10.2 cm) radius and arc of a circle of 7 inches (17.8 cm) radius. Figures 8 and 9 illustrate a titanium frame (26) similar to those of Figures 1 to 7 but having substantially parallel frame potions (27, 28) of different dimensions. The frame (26) is approximately 3.15 inches (8 cm) in length from the top of the second end portion (5) to the bottom of the first end portion (4). The substantially parallel frame portions (27, 28) each have four slots (7) in the frame edge (11) remote from the frame aperture (6), with the slots (7) being spaced approximately 0.55 inches (1.4 cm) apart and the slots closest to the second end portion (5) being approximately 0.86 inches (2.18 cm) from the top of the second end portion (5). Preferably, the frame (26) of Figures 8 and 9 is formed into frames of three different lordotic curvatures; flat, arc of a circle of 5 inches (13.2 cm) radius and arc of a circle of 7 inches (17.8 cm) radius. Figures 10 to 19 illustrate further alternative embodiments of the present invention. Figures 10, 11 and 12 illustrate titanium frames (41, 42, 43) similar to frames (26, 18, 1) of Figures 8, 6 and 1 respectively but having slots (44) in the frame end portions (4, 5). The frame end portions (4, 5) each have two slots (44) in the frame edge (11) remote from the frame aperture (6) in addition to the slots (7) in the parallel frame portions (2, 3). The embodiments of Figures 10, 11 and 12 do not have grooves in the frame edge (12) adjacent the frame aperture. Referring to Figures 13 and 14, an alternative titanium alloy frame (71) having first and second substantially parallel frame portions (72, 73) respectively, connected by first and second transverse bent (see Figure 17) shorter end frame portions (74, 75) respectively, defines a substantially bullet-shaped aperture (76) (see Figure 13) for receiving projecting spinal elements. The frame (71) is formed from titanium alloy (Ti-6Al-4V) sheet stock and has similar dimensions to those of the frames described above. The frame portions have a rectangular cross-section with chamfered corners (see Figure 18). The frame portions may alternatively be of rectangular cross-section with rounded corners (see Figure 19). Referring to Figure 13, the first frame end portion (74) curves slightly into the aperture (but is otherwise substantially straight) and the second frame end portion is substantially semi-circular (i.e. bent). An alternative construction of a frame similar to that of Figures 13 and 14 is shown in Figures 15 and 16. The parallel frame portions (82, 83) of the frame (81) curve as shown in Figure 16 so as to accommodate curvature of the spine (i.e. lordosis or kyphosis). In other respects the construction of the frame (81) of Figures 15 and 16 is similar to that of the frame (71) of Figures 13 and 14. As discussed above for the frame of Figure 1 the bullet shaped frames (71, 81) have superior conformance to the contours of the spine in comparison to the prior art spinal implants. The "tented" implant with a bullet shaped aperture has been found to fit more closely to the spine and hence reduces the dead space between the spine and the fixed implant. Such surgical implants have a curvature which mimics that of the spinal column so as to permit the implant to be fitted more closely, and, hence, more securely, around the vertebrae. The bullet shaped frame also leads to greater stability of the fixed implant as a result of an increased contact area between the fixed frame and bone. Using a frame of rectangular cross-section as described above leads to a further increased frame/bone contact area and hence to still greater stability. The generally rectangular cross-section provides more contact with the bony elements of the spine that the traditional prior art circular cross-section. A frame having the combination of both a bullet shape and with frame portions of rectangular cross-section is the most effective and stable implant construction.

Claims: A surgical implant for spinal fixation comprising a rigid biocompatible frame (1) defining an aperture (6), the frame consisting of first and second substantially parallel frame portions (2, 3) connected by bent third and fourth frame portions (4, 5) which oppose each other across the space between the first and second parallel frame portions and extend in the same direction as each other away from the plane defined by the first and second frame portions (2, 3), characterised by at least one of the third and fourth frame portions being curved (5) away from the opposing frame portion so as to define a tapered frame portion of relatively small width which, in use, can be fitted closely about the spine. A surgical implant according to Claim 1, wherein the third frame portion (5) is curved and the fourth frame portion (4) is substantially perpendicular to the parallel frame portions so as to define a substantially bullet shaped frame aperture (6). A surgical implant according to any of the preceding claims, wherein the frame portions each have a substantially rectangular cross section. A surgical implant according to Claim 3, wherein the edges of the frame portions are chamfered. A surgical implant according to any of the preceding claims, wherein the fourth frame portion (4) forms a shallow curve with the middle section of the fourth frame portion extending into the frame aperture. A surgical implant according to any of the preceding claims, wherein the first and second frame portions (2, 3) are curved so as to match the curvature of a portion of the spine. A surgical implant according to any of the preceding claims wherein the first and second frame portions (2, 3) are substantially straight. A surgical implant according to any of the preceding claims, wherein the frame (1) is formed from a titanium alloy.

Inventors: CROCKARD HUGH ALAN, MELOUL RAPHAELC, YAPP RONALD A, CROCKARD, HUGH ALAN, MELOUL, RAPHAEL, YAPP, RONALD A., Meloul, Raphaelc/o Codman &amp; Shurtkeff Inc.
Applicants: JOHNSON & JOHNSON PROFESSIONAL, JOHNSON & JOHNSON PROFESSIONAL INC.
Application year: 1994
Main classification: A61B17
IPC codes: A61B17